Dissipating Heat During Device Operation

ABSTRACT

Apparatus for dissipating heat during the operation of a device. In accordance with some embodiments, the apparatus compares spaced-apart first and second heat sources. A thermally conductive plate is disposed between the first and second heat sources. A thermal interface layer is contactingly disposed between the plate and the first heat source, and has a relatively higher thermal conductivity so that heat generated by the first heat source passes through the thermal interface layer and to the plate. A thermal barrier layer is contactingly disposed between the plate and the second heat source to mechanically support the plate relative to the second heat source. The thermal barrier layer has a relatively lower thermal conductivity to thermally isolate the conductive plate from the second heat source.

SUMMARY

Various embodiments of the present disclosure are generally directed toan apparatus which dissipates heat during operation of a device.

In accordance with some embodiments, the apparatus compares spaced-apartfirst and second heat sources. A thermally conductive plate is disposedbetween the first and second heat sources. A thermal interface layer iscontactingly disposed between the plate and the first heat source, andhas a relatively higher thermal conductivity so that heat generated bythe first heat source passes through the thermal interface layer and tothe plate. A thermal barrier layer is contactingly disposed between theplate and the second heat source to mechanically support the platerelative to the second heat source. The thermal barrier layer has arelatively lower thermal conductivity to thermally isolate theconductive plate from the second heat source.

These plus other features and aspects which characterize variousembodiments of the present disclosure can be understood in view of thefollowing detailed discussion and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a functional block representation of a data storagedevice in accordance with some embodiments of the present disclosure.

FIG. 2 is a perspective view of the storage device of FIG. 1 inaccordance with some embodiments.

FIGS. 3A-3C depict a thermal dissipation plate of the storage device ofFIG. 2 in accordance with some embodiments.

FIG. 4 provides a schematic representation of a thermal dissipationscheme in accordance with some embodiments.

FIG. 5 is a schematic representation of another thermal dissipationscheme in accordance with various embodiments.

FIG. 6 is a schematic representation of another thermal dissipationscheme in accordance with some embodiments.

FIG. 7 is a schematic representation of another thermal dissipationscheme in accordance with some embodiments.

DETAILED DESCRIPTION

Electronic devices can be susceptible to thermal effects duringoperation due to the generation of waste heat. If such heat is notproperly dissipated (transferred) away from a device, the device mayundergo undesired localized increases in operational temperature which,in turn, may affect device operation and reliability.

The transfer of heat from a device can be carried out by various meanssuch as conduction, convection and/or radiation. Generally, heatconduction describes the transfer of heat energy through a medium. Heatis a form of energy that manifests as molecular vibration, and so heatconduction generally involves kinetic energy transfer from one moleculeto another within a medium where the molecules otherwise remainsubstantially fixed in place.

By contrast, heat convection generally involves heat transfer through aliquid or gas through the displacement (e.g., circulation, migration,etc.) of molecules from a relatively higher temperature region to arelatively lower temperature region. Heat radiation generally involvesthe transmission of heat in the form of electromagnetic waves, such asinfrared waves, which are emitted from a first set of molecules andabsorbed by a second set of molecules at a distance from the first set.

Various embodiments of the present disclosure are generally directed toan apparatus for facilitating heat dissipation during the operation of adevice. As explained below, the apparatus includes spaced-apart firstand second heat sources and a thermally conductive plate disposedbetween the heat sources. A thermal interface layer is contactinglydisposed between the conductive plate and the first heat source. Thethermal interface layer has a relatively high thermal conductivity sothat heat generated by the first heat source passes through the thermalinterface material and to the conductive plate.

A thermal barrier layer is contactingly disposed between the conductiveplate and the second heat source. The thermal barrier layer has arelatively low thermal conductivity as compared to the thermalconductivity of the thermal interface layer. The thermal barrier layermechanically supports the plate relative to the second heat source, andthermally isolates the plate from the second heat source.

In some embodiments, the first heat source is an electronic componentsupported on a printed circuit board assembly (PCBA) of a data storagedevice, and the second heat source is a housing of the data storagedevice that houses at least one heat generating electrical component,such as a motor, a solid-state memory, etc. In further embodiments, thethermally conductive plate is elongated and includes cooling fins tofacilitate convection of heat transferred thereto through the thermalinterface material.

These and other features of various embodiments can be understoodbeginning with a review of FIG. 1 which provides a functional blockrepresentation of a data storage device 100. Please note that thepresentation of a data storage device is merely by way of illustrationand is not limiting to the scope of the present disclosure.

The device 100 includes a controller 102 and a memory 104. Thecontroller 102 can take a variety of forms such as a hardware basedcontrol circuit or a general purpose programmable processor havingsuitable programming to provide top level control for the device. Thememory 104 can take a variety of forms such as rotatable magnetic oroptical data recording media (discs), solid-state flash memory, hybridmemory modules (e.g., both rotatable and solid-state), etc.

FIG. 2 is a perspective underside representation of a data storagedevice 110 which corresponds to the device 100 of FIG. 1 in accordancewith some embodiments. The data storage device 110 is characterized as ahard disc drive (HDD) which employs magnetic recording media to storedata from a host device.

A housing 112 encloses various aspects of the device 110 including oneor more magnetic recording discs connected to a spindle motor, apreamplifier/driver circuit, transducer heads, a voice coil motor, etc.A boss projection 114 extends from a lower surface 116 of the housing112 to accommodate the spindle motor used to rotate the discs. Forreference, the housing 112 and those aspects enclosed therein aresometimes referred to as a head-disc assembly (HDA) 117.

A rigid printed circuit board assembly (PCBA) 118 is secured to the HDA117 and incorporates various electronic modules of the device 110 usedto control the HDA 117, such as a programmable controller, an interfacecircuit, a buffer, read and write channels, servo circuit, etc. Theseand other modules are represented by various integrated circuitcomponents 120 which are affixed to a rigid, multi-layer substrate 122(also referred to as a “printed circuit board,” or “PCB”). Acommunication assembly (not visible in FIG. 2) such as a flex circuit orbulkhead connector provides electrical interconnection between the HDA117 and the PCBA 118. An interface connector 124 of the PCBA 118 enablesinterconnection of the device 100 with a host (not separately shown).

The PCBA 118 is shown to be substantially rectangular for simplicity ofillustration. Other shapes and areal extents of the PCBA 118 can beused, including irregular shapes that at least partially surround theboss projection 114. In some cases, the PCBA 118 may substantially coverthe entire areal extent of the lower surface 116 of the housing 112, ora substantial portion thereof.

The storage device 110 further comprises a thermal dissipation assembly130 disposed between the HDA 117 and the PCBA 118, a portion of which isvisible in FIG. 2. Details concerning the thermal dissipation assembly130 will be presented below, but at this point it will be understoodthat the thermal dissipation assembly 130 secures the PCBA 118 to thehousing 112, conducts heat away from the PCBA 118 during deviceoperation, and thermally isolates the PCBA 118 from the HDA 117. In thisway, heat generated by the PCBA 118 can be efficiently removed from thePCBA, and heat generated by the HDA 117 will not tend to increase thetemperature of the PCBA (and vice versa). For reference, the

PCBA 118 is sometimes referred to herein as an exemplary “first heatsource” and the HDA 117 is sometimes referred to herein as an exemplary“second heat source.”

FIGS. 3A-3C depict a thermal dissipation (thermally conductive) plate132 of the thermal dissipation assembly 130 of FIG. 2 in accordance withsome embodiments. FIG. 3A is a top view of the plate 132, FIG. 3B is afront view of the plate 132, and FIG. 3C is a side cross-sectional viewof the plate 132 along lines 3C-3C in FIG. 3A.

The thermally conductive plate 132 is generally rectangular in shape andnominally corresponds to the areal extent of the PCBA 118 of FIG. 2.However, the plate 132 can take any suitable size or shape, includingsizes that are larger than or smaller than the PCBA 118. In someembodiments, the plate 132 extends to substantially cover the entirelower surface 116 of the housing (see FIG. 2) or a substantial portionthereof Notches, cutouts and other features can be supplied as required;for example, an aperture (not shown) may be supplied to facilitate aconnector that establishes electrical interconnection of the circuitryon the PCBA 118 with the HDA 117, etc.

The plate 132 is formed of a thermally conductive material, such asmetal(s) or metal alloy(s), and is generally rigid to provide amechanical support for the PCBA 118. In some embodiments, the plate 132is a layer of highly thermally conductive aluminum with a nominalthickness on the order of about 0.030 inches (30 mils) and a thermalconductivity of greater than about 100 W/mK (watts/meter*degree Kelvin).While the plate 132 is shown to have a substantially uniform thickness,localized relief and boss areas of varying thicknesses can be providedon the plate as required to adapt to contours of adjacent elements,provide mechanical rigidity, etc.

Other operational benefits may be supplied by the plate such aslocalized electromagnetic interference (EMI) shielding. The plate 132may be formed using any number of suitable processes such as stamping,rolling, casting, machining, molding, etc. Multiple pieces may beadjoined through welding, riveting, heat staking, etc. to provide aunitary plate. As used herein, a material will be considered to bethermally conductive if the material is provided with a thermalconductivity of at least about 1.0 W/mK . It is contemplated that theplate will be thermally conductive with a thermal conductivity of about1-300 W/mK or more.

Threaded apertures 134 extend through the plate 132 at suitablelocations to accommodate standoff/fastener assemblies (not separatelyshown) used to secure the PCBA 118 to the plate. A series ofspaced-apart cooling fins (projections) 136 extend along a leading edgeof the plate. The cooling fins 136 facilitate convective cooling of theplate responsive to air currents (depicted by arrow 138) that passadjacent the plate 132. The air currents may be generated throughnatural convection or through a forced air mechanism such as a nearbyelectric cooling fan, etc. The use of cooling fins is contemplated butnot required.

A pair of hook-shaped attachment members 140 are used to secure theplate 132 to the housing 112. The attachment members 140 take the formof hinge flanges which engage corresponding slots 142 in the housing 112(see FIG. 3C) to secure one end of the plate 132. The other end of theplate 132 can be secured using standoffs, adhesives, etc. Otherattachment configurations can be used to secure the plate 132 to thehousing 112 that do not utilize the hook-shaped attachment members 140.

FIG. 4 represents of the thermal dissipation assembly 130 in accordancewith some embodiments. The diagram is schematic in nature so that thevarious thicknesses, aspect ratios, etc. of the depicted components arenot drawn to scale. The thermal dissipation assembly 130 includes thethermal dissipation plate 132 from FIGS. 3A-3C sandwiched between athermal interface layer (TIL) 144 and a thermal barrier layer 146. Otherelements can be incorporated into the thermal dissipation assembly 130as required. For reference, the thermal interface layer 144 is sometimesreferred to as a thermal interface material.

The PCBA 118 is mechanically supported relative to the plate 132 using aseries of cylindrical standoffs 148 and corresponding threaded fasteners150. The fasteners 150 extend through the PCB 122 and the standoffs 148to engage the threaded apertures 134 in the plate 132. The plate 132 ismechanically supported relative to the housing 112 via theaforementioned hinge flanges 140 (FIG. 3C), the thermal barrier layer,and other securement members (not shown).

An integrated circuit (chip) 152 is supported on a lower side of the PCB122 opposite the side visible in FIG. 2. It is not necessarily requiredthat the PCBA 118 be a double-sided assembly, that is, it is notrequired that circuit components (e.g. 120, 152) be disposed on both thetop and bottom sides of the PCB 122. It is contemplated that the chip152 is a processing type device that consumes a relatively large amountof electrical power and, in turn, generates a significant amount of heatduring operation. An intervening substrate, carrier or other mechanismmay support the chip 140 relative to the PCB 122, but such has beenomitted from the FIG. 4.

The thermal interface layer (TIL) 144 contactingly engages a distalsurface of the chip 152 opposite the PCB 122. The TIL 144 may cover theentirety of the areal extent of the chip 152, or a substantial portionthereof as required. The TIL 144 has a relatively high thermalconductivity and provides a thermally conductive path from the chip 152to the plate 132. While not limiting, it is contemplated that the TIL144 has a thermal conductivity of at least about 1.0 W/mK. The TIL 144can take a variety of forms, including a flexible electricallyinsulative, thermally conductive layer; a thermal grease; a thermalbond; a thermally conductive silicone pad; a thermally conductive tape;a graphite sheet; a thermally conductive phase change material; athermoplastic material, a metal layer, etc. If formed of metal, the TIL144 may comprise a layer of aluminum, copper, silver, etc.

During operation, heat conductively flows from the chip 152, through theTIL 144 and to the plate 132 as represented by arrows 154. The mass ofthe plate 132 is significantly greater than that of the TIL 144, and hasa relatively large surface area to facilitate convective cooling as heatpasses from the plate 132 to the surrounding atmospheric air asrepresented by arrow 156. The use of the cooling fins 136 (FIGS. 3A-3C)and/or forced airflow (e.g., 138 in FIG. 3A) can enhance the convectivecooling of the plate 132, which lowers the temperature of the plate andincreases the rate of heat conduction through the TIL 144.

The thermal barrier layer 146 mechanically supports and thermallyisolates the plate 132 from the housing 112. The thermal barrier layer146 can take a variety of constructions such as but not limited toflexible or rigid polymers, ceramics, thermally conductive materials,electrically insulative materials, compressive pads, glass, etc. In somecases, the layer 146 is non-thermally conductive material, such as onehaving a thermal conductivity of less than about 1.0 W/mK. In othercases, the layer 146 is thermally conductive (e.g., equal to or greaterthan about 1.0 W/mK) but at a level less than the thermal conductivityof the TIL 144. For example, the thermal conductivity of the TIL 144 maybe a multiple of (e.g., 3×, 5×, etc.) the thermal conductivity of thebarrier layer 146. It is contemplated that the thermal conductivity ofthe plate 132 will be significantly greater than that of both the TIL144 and the thermal barrier layer 146.

Those skilled in the art will recognize that heat in a system willgenerally tend to flow, through conduction, convection and/or radiation,from a higher temperature zone to a lower temperature zone. Depending onthe configuration of the system of FIG. 4, substantial amounts of heatmay be generated by the HDA 117, and the housing 112 may increase intemperature as a result. The housing has a relatively large mass andsurface area and so it is contemplated that a portion of this waste heatwill tend to be convectively transferred to the surrounding air, asgenerally denoted by arrow 158.

In some cases, this heat may be convectively transferred across theintervening air gap between the plate 132 and the housing 112. However,because air is generally non-thermally conductive (e.g., about 0.025W/mK), and because the thermal barrier layer 146 has a relatively lowthermal conductivity, the rate of heat transfer to the plate 132 fromthe chip will tend to be significantly greater than the amount (if any)of heat transfer to the plate from the housing 112. In this way, thethermal barrier layer 146 will tend to thermally isolate the plate 132(and hence, the chip 152) from the housing 112, and vice versa.

While not necessarily limiting, the thermal conductivity of the thermalbarrier 146 in some cases is selected to be equal to or less than thatof atmospheric air. In other cases, the thermal conductivity of thethermal barrier 146 is selected to be greater than that of atmosphericair but less than that of the TIL 144 and the plate 132. In stillfurther cases, the TIL 142 and the thermal barrier layer 146 share acommon construction but the thermal barrier layer 146 is substantiallythicker than the TIL 144, and so the thermal barrier layer 146 has anoverall lower thermal conductivity as compared to the TIL 144.

FIG. 5 is a schematic depiction of a generalized system 160 thatoperates in a manner similar to the arrangement of FIG. 4. The system160 includes a first heat source 162, a second heat source 164, and athermal dissipation assembly 166 comprising a thermal interface layer168, a thermally conductive plate (heat sink) 170 and a thermal barrierlayer 172. The respective sizes and areal extents of the respectiveelements can vary. As noted above, the thermal interface layer 168facilitates the efficient conduction of heat from the first heat source162 to the plate 170, and the thermal barrier layer mechanicallysupports and thermally isolates the plate 170 from the second heatsource 164.

FIG. 6 illustrates another data storage device 180 in accordance withsome embodiments. The data storage device 180 is similar to the device110 discussed above. As before, the sizes and aspect ratios representedin FIG. 6 are merely for purposes of illustration and are not drawn toscale.

The device 180 includes a housing 182 which encloses a memory element184, and a printed circuit board assembly (PCBA) 186 that suppliescontrol electronics for the memory element 184 as well as other elementsdisposed within the housing. The PCBA 186 includes a planar printedcircuit board (PCB) 188 and at least one integrated circuit (chip) 190supported by a ball grid array (BGA) interconnection mechanism 192. Asbefore, it is contemplated that the PCBA 186 in general, and the chip190 in particular, is a source of heat and may undergo a significantincrease in temperature during operation.

A thermal dissipation assembly 200 includes first and second layers ofthermal interface material 202, 204 (referred to as “first TIL” and“second TIL,” respectively) and an intervening thermally conductiveplate 206. In some embodiments, the first and second TIL layers 202, 204each generally comprise flexible sheets of electrically insulative andthermally conductive material.

In some cases, the respective layers 202, 204 share a common overallconstruction, but the second TIL 204 is thicker than the first first TIL202 so that the overall thermal conductivity of the second TIL is lowerthan that of the first TIL. As with the other embodiments discussedabove, the respective TIL layers can each comprise a single layer ormultiple layers of the same or different material.

The thermal dissipation assembly 200 further includes opposing foamspacers 208, 210 which are compressed between the housing 182 and thePCB 188 and contactingly engage and retain the respective TIL layers202, 204 and the plate 206. The foam spacers 208, 210 are open or closedcell foam members of electrically insulating material. The spacers 208,210 can be arranged on opposing sides of the plate 206 as shown, or cansurround additional sides. Generally, however, it is contemplated thatat least one side will remain open and exposed to the surroundingenvironment for purposes of heat convection from the plate 206. Othertypes of retention features can be used used in lieu of the foam spacers208, 210.

As before, heat generated by the chip 190 is conducted through the firstTIL 202 to the plate 206, and the second TIL 204 serves as a thermalbarrier to thermally isolate the plate 206 from the housing 182.Although not shown in FIG. 6, the plate 206 can have the same arealextent as the respective TIL layers 202, 204, or can extend beyond theTIL layers 202, 204 to provide additional exposed airflow contact tofacilitate convective cooling.

The arrangement of FIG. 6 is particularly suitable for low profileapplications where a relatively small amount of space is availablebetween the PCBA 186 and the housing 182.

In some embodiments, the distance D1 from the PCB 188 to the housing 182is about 0.136 inches (136 mils), the distance D2 from a facing surfaceof the PCB 188 to a facing surface of the chip 190 is about 0.053 inches(53 mils), and the distance from the facing surface of the chip 190 tothe housing 182 is about 0.083 inches (83 mils).

In some cases, the arrangement of FIG. 6 is configured to maintain anoperational temperature of the chip 190 at a level of about 45 degreesCelsius or lower. In other cases, the arrangement of FIG. 6 isconfigured to maintain an operational temperature of the chip 190 at alevel equal to or lower than that of the housing 182.

FIG. 7 is a schematic representation of another system 220 in accordancewith some embodiments. In this configuration, a PCBA 222 includes a PCB224 which supports a first electronic component (chip 1) 226 and asecond electronic component (chip 2) 228. The PCBA 222 provides controlelectronics for an adjacent head disc assembly (HDA) 230.

A thermal dissipation assembly 232 is interposed between the PCBA 222and the HDA 230 and includes a thermally conductive plate 234; first andsecond thermal interface material (TIL) layers 236, 238 that arecontactingly disposed between the respective chips 226, 228 and theplate 234; and first and second thermal barrier layers 240, 242contactingly disposed between the plate 234 and the HDA 230. Moregenerally, any suitable respective numbers of thermal interface layersand thermal barrier layers can be used, including different numbers ofeach, and the respective layers can be placed in various axially aligned(e.g., 236, 240) or non-aligned (e.g., 238, 242) locations as required.

In FIG. 7, the respective first and second TIL layers 236, 238 may sharea common thermal conductivity, or may have different thermalconductivities in relation to differences in the amount of heatgenerated by the respective chips 226, 228. As before, the thermalbarrier layers 240, 242 each have a thermal conductivity less than thoseof the first and second TIL layers 236, 238 and thermally isolate theplate 234 from the HDA 230. The relatively high thermal impedance(s) ofthe barrier layers 240, 242 effectively provide thermal isolationbetween the HDA 230 and the plate 234, while the relatively low thermalimpedance(s) of the TIL layers 236, 238 provide efficient conduction ofheat from the chips 226, 228 to the plate 234.

While the various embodiments described herein have been in theenvironment of a data storage device, such is merely illustrative andnot limiting. Any number of different types of electrical, electronic,and/or heat generating devices can be configured to incorporate thefeatures of the various disclosed embodiments as desired.

It is to be understood that even though numerous characteristics andadvantages of various embodiments of the present disclosure have beenset forth in the foregoing description, together with details of thestructure and function of various embodiments disclosed, this detaileddescription is illustrative only, and changes may be made in detail,especially in matters of structure and arrangements of parts within theprinciples of the present disclosure to the full extent indicated by thebroad general meaning of the terms in which the appended claims areexpressed.

What is claimed is:
 1. An apparatus comprising: spaced-apart first andsecond heat sources; a thermally conductive plate disposed between thefirst and second heat sources; a thermal interface layer contactinglydisposed between the plate and the first heat source and having arelatively higher thermal conductivity so that heat generated by thefirst heat source passes through the thermal interface layer and to theplate; and a thermal barrier layer contactingly disposed between theplate and the second heat source to mechanically support the platerelative to the second heat source, the thermal barrier layer having arelatively lower thermal conductivity to thermally isolate theconductive plate from the second heat source.
 2. The apparatus of claim1, wherein the first heat source comprises a printed circuit boardassembly (PCBA) having at least one electrical component, and whereinthe thermal interface material contactingly engages a surface of the atleast one electrical component to provide a heat transfer path from theat least one electrical component to the conductive plate.
 3. Theapparatus of claim 1, wherein the conductive plate comprises a pluralityof spaced apart cooling fins to facilitate convection of heattransferred thereto from the first heat source.
 4. The apparatus ofclaim 1, wherein the thermal interface layer comprises a flexible layerof heat conductive, electrically insulative material.
 5. The apparatusof claim 4, wherein the thermal barrier layer comprises a flexible layerof heat conductive, electrically insulative material.
 6. The apparatusof claim 1, wherein the thermal interface layer and the thermal barrierlayer share a common construction and wherein the thermal interfacelayer is thicker than the thermal barrier layer so that a differencebetween the relatively lower thermal conductivity of the thermal barrierlayer and the relatively higher thermal conductivity of the thermalinterface layer is in relation to a difference in thickness between thethermal barrier layer and the thermal interface layer.
 7. The apparatusof claim 1, further comprising a resilient support member contactinglyadjacent the plate, wherein the first and second heat sourcescompressingly engage the resilient support member.
 8. The apparatus ofclaim 8, wherein the resilient support member comprises a foam spacer.9. The apparatus of claim 1, wherein the thermal interface layer has athermal conductivity of at least about 1 W/mK, the thermal barrier layerhas a thermal conductivity of less than about 1 W/mK
 10. The apparatusof claim 9, wherein the plate has a thermal conductivity greater thanthe thermal conductivity of the thermal interface layer.
 11. Theapparatus of claim 1, further comprising a first attachment mechanismthat rigidly secures the first heat source to the plate, and a secondattachment mechanism that rigidly secures the plate to the second heatsource.
 12. An apparatus comprising: a printed circuit board assembly(PCBA) comprising a planar printed circuit board (PCB) supporting anintegrated circuit component; a housing member; and a thermaldissipation assembly disposed between the PCBA and the housing member,comprising: a thermal interface layer contactingly engaging theintegrated circuit component and having a first thermal conductivity; athermal barrier layer contactingly engaging the housing member andhaving a second thermal conductivity lower than the first thermalconductivity; and a thermally conductive plate contactingly disposedbetween the thermal interface layer and the thermal barrier layer. 13.The apparatus of claim 12, wherein the plate has a first plate surfacein facing relation to and nominally parallel to a first PCB surface ofthe PCB, and an opposing second plate surface in facing relation to andnominally parallel to a first housing surface of the housing member. 14.The apparatus of claim 13, wherein the first plate surface has anoverall areal extent that nominally corresponds to an overall arealextent of the first PCB surface.
 15. The apparatus of claim 13, whereinthe first plate surface has an overall areal extent that is smaller thanan overall areal extent of the first PCB surface.
 16. The apparatus ofclaim 13, wherein an overall distance from the first PCB surface to thefirst housing surface is less than about 0.150 inches.
 17. The apparatusof claim 12, wherein the thermal interface layer comprises a firstflexible layer of heat conductive, electrically insulative material, andthe thermal barrier layer comprises a second flexible layer of heatconductive, electrically insulative material.
 18. The apparatus of claim17, wherein the first flexible layer and the second flexible layer areboth the same material, and wherein the second flexible layer is thickerthan the first flexible layer in a direction from the PCBA to thehousing member.
 19. The apparatus of claim 12, further comprising aresilient support member contactingly adjacent the plate, wherein thefirst and second heat sources compressingly engage the resilient supportmember.
 20. The apparatus of claim 12, further comprising a firstplurality of spaced-apart thermal interface layers contactingly disposedbetween the PCBA and the plate, and a second plurality of spaced-apartthermal barrier layers contactingly disposed between the plate and thehousing member, wherein each of the second plurality of spaced-apartthermal barrier layers has a thermal conductivity less than the thermalconductivities of each of the first plurality of spaced-apart thermalinterface layers.